Welcome to LLVM! In order to get started, you first need to know some
basic information.

First, LLVM comes in two pieces. The first piece is the LLVM suite. This
contains all of the tools, libraries, and header files needed to use the low
level virtual machine. It contains an assembler, disassembler, bytecode
analyzer, and bytecode optimizer. It also contains a test suite that can be
used to test the LLVM tools and the GCC front end.

The second piece is the GCC front end. This component provides a version of
GCC that compiles C and C++ code into LLVM bytecode. Currently, the GCC front
end is a modified version of GCC 3.4 (we track the GCC 3.4 development). Once
compiled into LLVM bytecode, a program can be manipulated with the LLVM tools
from the LLVM suite.

There is a third, optional piece called llvm-test. It is a suite of programs
with a testing harness that can be used to further test LLVM's functionality
and performance.

Notes:1 Code generation supported for Pentium processors and up2 Code generation supported for 32-bit ABI only3 No native code generation4 Build is not complete: one or more tools don't link5 The GCC-based C/C++ frontend does not build

Note that you will need about 1-3 GB of space for a full LLVM build in Debug
mode, depending on the system (because of all the debug info), and the libraries
appear in more than one of the tools that get linked, so there is some
duplication. If you do not need many of the tools and you are space-conscious,
you can disable them individually in llvm/tools/Makefile. The Release
build requires considerably less space.

The LLVM suite may compile on other platforms, but it is not
guaranteed to do so. If compilation is successful, the LLVM utilities should be
able to assemble, disassemble, analyze, and optimize LLVM bytecode. Code
generation should work as well, although the generated native code may not work
on your platform.

The GCC front end is not very portable at the moment. If you want to get it
to work on another platform, you can download a copy of the source and try to compile it on your platform.

Compiling LLVM requires that you have several software packages
installed. The table below lists those required packages. The Package column
is the usual name for the software package that LLVM depends on. The Version
column provides "known to work" versions of the package. The Notes column
describes how LLVM uses the package and provides other details.

LLVM is very demanding of the host C++ compiler, and as such tends to expose
bugs in the compiler. In particular, several versions of GCC crash when trying
to compile LLVM. We routinely use GCC 3.3.3 and GCC 3.4.0 and have had success
with them. Other versions of GCC will probably work as well. GCC versions listed
here are known to not work. If you are using one of these versions, please try
to upgrade your GCC to something more recent. If you run into a problem with a
version of GCC not listed here, please let
us know. Please use the "gcc -v" command to find out which version
of GCC you are using.

GCC versions prior to 3.0: GCC 2.96.x and before had several
problems in the STL that effectively prevent it from compiling LLVM.

GCC 3.2.2: This version of GCC fails to compile LLVM.

GCC 3.3.2: This version of GCC suffered from a serious bug which causes it to crash in
the "convert_from_eh_region_ranges_1" GCC function.

The remainder of this guide is meant to get you up and running with
LLVM and to give you some basic information about the LLVM environment.

The later sections of this guide describe the general layout of the the LLVM source tree, a simple example using the LLVM tool chain, and links to find more information about LLVM or to get
help via e-mail.

Throughout this manual, the following names are used to denote paths
specific to the local system and working environment. These are not
environment variables you need to set but just strings used in the rest
of this document below. In any of the examples below, simply replace
each of these names with the appropriate pathname on your local system.
All these paths are absolute:

SRC_ROOT

This is the top level directory of the LLVM source tree.

OBJ_ROOT

This is the top level directory of the LLVM object tree (i.e. the
tree where object files and compiled programs will be placed. It
can be the same as SRC_ROOT).

LLVMGCCDIR

This is the where the LLVM GCC Front End is installed.

For the pre-built GCC front end binaries, the LLVMGCCDIR is
cfrontend/platform/llvm-gcc.

In order to compile and use LLVM, you will need to set some environment
variables. There are also some shell aliases which you may find useful.
You can set these on the command line, or better yet, set them in your
.cshrc or .profile.

LLVM_LIB_SEARCH_PATH=LLVMGCCDIR/bytecode-libs

This environment variable helps the LLVM GCC front end find bytecode
libraries that it will need for compilation.

alias llvmgcc LLVMGCCDIR/bin/gcc

alias llvmg++ LLVMGCCDIR/bin/g++

These aliases allow you to use the LLVM C and C++ front ends without putting
them in your PATH or typing in their complete pathnames.

If you have the LLVM distribution, you will need to unpack it before you
can begin to compile it. LLVM is distributed as a set of two files: the LLVM
suite and the LLVM GCC front end compiled for your platform. There is an
additional test suite that is optional. Each file is a TAR archive that is
compressed with the gzip program.

Before configuring and compiling the LLVM suite, you need to extract the LLVM
GCC front end from the binary distribution. It is used for building the
bytecode libraries later used by the GCC front end for linking programs, and its
location must be specified when the LLVM suite is configured.

To install the GCC front end, do the following:

cd where-you-want-the-front-end-to-live

gunzip --stdout cfrontend-version.platform.tar.gz | tar -xvf
-

Next, you will need to fix your system header files:

cd cfrontend/platform
./fixheaders

The binary versions of the GCC front end may not suit all of your needs. For
example, the binary distribution may include an old version of a system header
file, not "fix" a header file that needs to be fixed for GCC, or it may be
linked with libraries not available on your system.

Once checked out from the CVS repository, the LLVM suite source code must be
configured via the configure script. This script sets variables in the
various *.in files, most notably llvm/Makefile.config and
llvm/include/Config/config.h. It also populates OBJ_ROOT with
the Makefiles needed to begin building LLVM.

The following environment variables are used by the configure
script to configure the build system:

Variable

Purpose

CC

Tells configure which C compiler to use. By default,
configure will look for the first GCC C compiler in
PATH. Use this variable to override
configure's default behavior.

CXX

Tells configure which C++ compiler to use. By default,
configure will look for the first GCC C++ compiler in
PATH. Use this variable to override
configure's default behavior.

The following options can be used to set or enable LLVM specific options:

--with-llvmgccdir=LLVMGCCDIR

Path to the location where the LLVM GCC front end binaries and
associated libraries were installed. This must be specified as an
absolute pathname.

--with-tclinclude

Path to the tcl include directory under which the tclsh can be
found. Use this if you have multiple tcl installations on your machine and you
want to use a specific one (8.x) for LLVM. LLVM only uses tcl for running the
dejagnu based test suite in llvm/test. If you don't specify this
option, the LLVM configure script will search for tcl 8.4 and 8.3 releases.

--enable-optimized

Enables optimized compilation by default (debugging symbols are removed
and GCC optimization flags are enabled). The default is to use an
unoptimized build (also known as a debug build).

--enable-jit

Compile the Just In Time (JIT) compiler functionality. This is not
available
on all platforms. The default is dependent on platform, so it is best
to explicitly enable it if you want it.

--enable-doxygen

Look for the doxygen program and enable construction of doxygen based
documentation from the source code. This is disabled by default because
generating the documentation can take a long time and producess 100s of
megabytes of output.

To configure LLVM, follow these steps:

Change directory into the object root directory:
cd OBJ_ROOT

Run the configure script located in the LLVM source tree:
SRC_ROOT/configure --prefix=/install/path [other options]

In addition to running configure, you must set the
LLVM_LIB_SEARCH_PATH environment variable in your startup shell
scripts. This environment variable is used to locate "system" libraries like
"-lc" and "-lm" when linking. This variable should be set to
the absolute path of the bytecode-libs subdirectory of the GCC front
end, or LLVMGCCDIR/bytecode-libs. For example, one might set
LLVM_LIB_SEARCH_PATH to
/home/vadve/lattner/local/x86/llvm-gcc/bytecode-libs for the x86
version of the GCC front end on our research machines.

Once you have configured LLVM, you can build it. There are three types of
builds:

Debug Builds

These builds are the default when one types gmake (unless the
--enable-optimized option was used during configuration). The
build system will compile the tools and libraries with debugging
information.

Release (Optimized) Builds

These builds are enabled with the --enable-optimized option to
configure or by specifying ENABLE_OPTIMIZED=1 on the
gmake command line. For these builds, the build system will
compile the tools and libraries with GCC optimizations enabled and strip
debugging information from the libraries and executables it generates.

Profile Builds

These builds are for use with profiling. They compile profiling
information into the code for use with programs like gprof.
Profile builds must be started by specifying ENABLE_PROFILING=1
on the gmake command line.

Once you have LLVM configured, you can build it by entering the
OBJ_ROOT directory and issuing the following command:

gmake

If the build fails, please check here to see if you
are using a version of GCC that is known not to compile LLVM.

If you have multiple processors in your machine, you may wish to use some of
the parallel build options provided by GNU Make. For example, you could use the
command:

gmake -j2

There are several special targets which are useful when working with the LLVM
source code:

gmake clean

Removes all files generated by the build. This includes object files,
generated C/C++ files, libraries, and executables.

gmake dist-clean

Removes everything that gmake clean does, but also removes files
generated by configure. It attempts to return the source tree to the
original state in which it was shipped.

gmake install

Installs LLVM header files, libraries, tools, and documentation in a
hierarchy
under $PREFIX, specified with ./configure --prefix=[dir], which
defaults to /usr/local.

gmake -C runtime install-bytecode

Assuming you built LLVM into $OBJDIR, when this command is run, it will
install bytecode libraries into the GCC front end's bytecode library
directory. If you need to update your bytecode libraries,
this is the target to use once you've built them.

Please see the Makefile Guide for further
details on these make targets and descriptions of other targets
available.

It is also possible to override default values from configure by
declaring variables on the command line. The following are some examples:

gmake ENABLE_OPTIMIZED=1

Perform a Release (Optimized) build.

gmake ENABLE_PROFILING=1

Perform a Profiling build.

gmake VERBOSE=1

Print what gmake is doing on standard output.

gmake TOOL_VERBOSE=1

Ask each tool invoked by the makefiles to print out what it is doing on
the standard output. This also implies VERBOSE=1.

Every directory in the LLVM object tree includes a Makefile to build
it and any subdirectories that it contains. Entering any directory inside the
LLVM object tree and typing gmake should rebuild anything in or below
that directory that is out of date.

The LLVM build system is capable of sharing a single LLVM source tree among
several LLVM builds. Hence, it is possible to build LLVM for several different
platforms or configurations using the same source tree.

This is accomplished in the typical autoconf manner:

Change directory to where the LLVM object files should live:

cd OBJ_ROOT

Run the configure script found in the LLVM source
directory:

SRC_ROOT/configure

The LLVM build will place files underneath OBJ_ROOT in directories
named after the build type:

If you're running on a linux system that supports the "
binfmt_misc"
module, and you have root access on the system, you can set your system up to
execute LLVM bytecode files directly. To do this, use commands like this (the
first command may not be required if you are already using the module):

This directory contains public header files exported from the LLVM
library. The three main subdirectories of this directory are:

llvm/include/llvm

This directory contains all of the LLVM specific header files. This
directory also has subdirectories for different portions of LLVM:
Analysis, CodeGen, Target, Transforms,
etc...

llvm/include/llvm/Support

This directory contains generic support libraries that are provided with
LLVM but not necessarily specific to LLVM. For example, some C++ STL utilities
and a Command Line option processing library store their header files here.

llvm/include/llvm/Config

This directory contains header files configured by the configure
script. They wrap "standard" UNIX and C header files. Source code can
include these header files which automatically take care of the conditional
#includes that the configure script generates.

This directory contains files that describe various target architectures
for code generation. For example, the llvm/lib/Target/SparcV9
directory holds the Sparc machine description while
llvm/lib/Target/CBackend implements the LLVM-to-C converter

llvm/lib/CodeGen/

This directory contains the major parts of the code generator: Instruction
Selector, Instruction Scheduling, and Register Allocation.

llvm/lib/Debugger/

This directory contains the source level debugger library that makes
it possible to instrument LLVM programs so that a debugger could identify
source code locations at which the program is executing.

llvm/lib/ExecutionEngine/

This directory contains libraries for executing LLVM bytecode directly
at runtime in both interpreted and JIT compiled fashions.

llvm/lib/Support/

This directory contains the source code that corresponds to the header
files located in llvm/include/Support/.

llvm/lib/System/

This directory contains the operating system abstraction layer that
shields LLVM from platform-specific coding.

This directory contains projects that are not strictly part of LLVM but are
shipped with LLVM. This is also the directory where you should create your own
LLVM-based projects. See llvm/projects/sample for an example of how
to set up your own project. See llvm/projects/Stacker for a fully
functional example of a compiler front end.

This directory contains libraries which are compiled into LLVM bytecode and
used when linking programs with the GCC front end. Most of these libraries are
skeleton versions of real libraries; for example, libc is a stripped down
version of glibc.

Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front
end to compile.

This is not a directory in the normal llvm module; it is a separate CVS
module that must be checked out (usually to projects/llvm-test). This
module contains a comprehensive correctness, performance, and benchmarking
test
suite for LLVM. It is a separate CVS module because not every LLVM user is
interested in downloading or building such a comprehensive test. For further
details on this test suite, please see the
Testing Guide document.

The tools directory contains the executables built out of the
libraries above, which form the main part of the user interface. You can
always get help for a tool by typing tool_name --help. The
following is a brief introduction to the most important tools. More detailed
information is in the Command Guide.

analyze

analyze is used to run a specific
analysis on an input LLVM bytecode file and print out the results. It is
primarily useful for debugging analyses, or familiarizing yourself with
what an analysis does.

bugpoint

bugpoint is used to debug
optimization passes or code generation backends by narrowing down the
given test case to the minimum number of passes and/or instructions that
still cause a problem, whether it is a crash or miscompilation. See HowToSubmitABug.html for more information
on using bugpoint.

llvmc

The LLVM Compiler Driver. This program can
be configured to utilize both LLVM and non-LLVM compilation tools to enable
pre-processing, translation, optimization, assembly, and linking of programs
all from one command line. llvmc also takes care of processing the
dependent libraries found in bytecode. This reduces the need to get the
traditional -l<name> options right on the command line. Please
note that this tool is new in 1.4 and considered experimental. It will be
fully supported in 1.5.

llvm-ar

The archiver produces an archive containing
the given LLVM bytecode files, optionally with an index for faster
lookup.

llvm-ld is very similar to gccld and provides a general purpose
and extensible linker for LLVM. This is the linker invoked by llvmc.
It allows optimization modules to be loaded so that language specific
optimizations can be applied at link time. Please note that this tool is new
in LLVM 1.4 and still considered experimental. It will be fully supported in
LLVM 1.5.

llvm-link

llvm-link, not surprisingly, links multiple LLVM modules into
a single program.

lli

lli is the LLVM interpreter, which
can directly execute LLVM bytecode (although very slowly...). In addition
to a simple interpreter, lli also has a tracing mode (entered by
specifying -trace on the command line). Finally, for
architectures that support it (currently x86, Sparc, and PowerPC), by default,
lli will function as a Just-In-Time compiler (if the
functionality was compiled in), and will execute the code much
faster than the interpreter.

llc

llc is the LLVM backend compiler, which
translates LLVM bytecode to a SPARC or x86 assembly file, or to C code (with
the -march=c option).

llvmgcc

llvmgcc is a GCC-based C frontend
that has been retargeted to emit LLVM code as the machine code output. It
works just like any other GCC compiler, taking the typical -c, -S, -E,
-o options that are typically used. The source code for the
llvmgcc tool is currently not included in the LLVM CVS tree
because it is quite large and not very interesting.

gccas

This tool is invoked by the llvmgcc frontend as the
"assembler" part of the compiler. This tool actually assembles LLVM
assembly to LLVM bytecode, performs a variety of optimizations, and
outputs LLVM bytecode. Thus when you invoke
llvmgcc -c x.c -o x.o, you are causing gccas to be
run, which writes the x.o file (which is an LLVM bytecode file
that can be disassembled or manipulated just like any other bytecode
file). The command line interface to gccas is designed to be
as close as possible to the system `as' utility so that
the gcc frontend itself did not have to be modified to interface to
a "weird" assembler.

gccld

gccld links together several LLVM bytecode files into one
bytecode file and does some optimization. It is the linker invoked by
the GCC frontend when multiple .o files need to be linked together.
Like gccas, the command line interface of gccld is
designed to match the system linker, to aid interfacing with the GCC
frontend.

opt

opt reads LLVM bytecode, applies a
series of LLVM to LLVM transformations (which are specified on the command
line), and then outputs the resultant bytecode. The 'opt --help'
command is a good way to get a list of the program transformations
available in LLVM.

This directory contains utilities for working with LLVM source code, and some
of the utilities are actually required as part of the build process because they
are code generators for parts of LLVM infrastructure.

Burg/

Burg is an instruction selector
generator -- it builds trees on which it then performs pattern-matching to
select instructions according to the patterns the user has specified. Burg
is currently used in the Sparc V9 backend.

codegen-diff

codegen-diff is a script
that finds differences between code that LLC generates and code that LLI
generates. This is a useful tool if you are debugging one of them,
assuming that the other generates correct output. For the full user
manual, run `perldoc codegen-diff'.

cvsupdate

cvsupdate is a script that will
update your CVS tree, but produce a much cleaner and more organized output
than simply running `cvs -z3 up -dP' will. For example, it will group
together all the new and updated files and modified files in separate
sections, so you can see at a glance what has changed. If you are at the
top of your LLVM CVS tree, running utils/cvsupdate is the
preferred way of updating the tree.

emacs/

The emacs directory contains
syntax-highlighting files which will work with Emacs and XEmacs editors,
providing syntax highlighting support for LLVM assembly files and TableGen
description files. For information on how to use the syntax files, consult
the README file in that directory.

getsrcs.sh

The getsrcs.sh script finds
and outputs all non-generated source files, which is useful if one wishes
to do a lot of development across directories and does not want to
individually find each file. One way to use it is to run, for example:
xemacs `utils/getsources.sh` from the top of your LLVM source
tree.

llvmgrep

This little tool performs an "egrep -H -n" on each source file in LLVM and
passes to it a regular expression provided on llvmgrep's command
line. This is a very efficient way of searching the source base for a
particular regular expression.

makellvm

The makellvm script compiles all
files in the current directory and then compiles and links the tool that
is the first argument. For example, assuming you are in the directory
llvm/lib/Target/Sparc, if makellvm is in your path,
simply running makellvm llc will make a build of the current
directory, switch to directory llvm/tools/llc and build it,
causing a re-linking of LLC.

NightlyTest.pl and
NightlyTestTemplate.html

These files are used in a
cron script to generate nightly status reports of the functionality of
tools, and the results can be seen by following the appropriate link on
the LLVM homepage.

TableGen/

The TableGen directory contains
the tool used to generate register descriptions, instruction set
descriptions, and even assemblers from common TableGen description
files.

vim/

The vim directory contains
syntax-highlighting files which will work with the VIM editor, providing
syntax highlighting support for LLVM assembly files and TableGen
description files. For information on how to use the syntax files, consult
the README file in that directory.

This directory contains build scripts and project files for use with
Visual C++. This allows developers on Windows to build LLVM without the need
for Cygwin. The contents of this directory should be considered experimental
at this time.

Note that you should have already built the tools and they have to be
in your path, at least gccas and gccld.

This will create two result files: hello and
hello.bc. The hello.bc is the LLVM bytecode that
corresponds the the compiled program and the library facilities that it
required. hello is a simple shell script that runs the bytecode
file with lli, making the result directly executable. Note that
all LLVM optimizations are enabled by default, so there is no need for a
"-O3" switch.

Run the program. To make sure the program ran, execute one of the
following commands:

This document is just an introduction to how to use LLVM to do
some simple things... there are many more interesting and complicated things
that you can do that aren't documented here (but we'll gladly accept a patch
if you want to write something up!). For more information about LLVM, check
out: